Double seal bearing

ABSTRACT

A double seal bearing includes a labyrinth seal mechanism. The double seal bearing is provided with a pair of annular inner and outer sealing plates having respective central openings with a remaining slight clearance between each respective sealing plate and one of the inner and outer races, respectively, so as to assure the labyrinth seal function.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates in particular to a double seal bearing including a pair of sealing plates of non-contacting type on at least one side thereof, more particularly a double seal ball bearing especially suitable for the spindle motor of the hard disk drive means.

2. Description of the Prior Art

The bearing illustrated in FIG. 11 includes a sealing structure of non-contacting type of the prior art.

This sealing structure of non-contacting type of the prior art includes at least on one end thereof a sealing plate 11. This sealing structure is of the non-contacting type in which the outer peripheral edge of the sealing plate 11 is secured on the end surface of the outer race 2, whereas the inner peripheral edge of this sealing plate is separated from the outer peripheral surface of the inner race 1.

A disadvantage inherent in the bearing of non-contacting type is that the grease contained within the bearing and dust or other contaminant produced within the bearing tend to flow out through the clearance formed at the non contacting portion of the bearing while the inner or outer race is rotated.

In general, the following countermeasures have been taken to eliminate the above mentioned disadvantage.

(1) One of the countermeasures is to make the inner peripheral edge 12 a of the sealing plate contact with the outer peripheral surface of the inner race 1 as shown in FIG. 12.

(2) The other of the countermeasures is to provide an oil seal (the seal of contacting type) or a labyrinth seal mechanism of non-contacting type for avoiding the flowing out of the grease or dusts.

However, the following problems or disadvantages are present in these countermeasures.

(1) As for the bearing including a sealing structure of the contacting type in which the inner peripheral edge of the sealing plate contacts with the inner race, there are problems listed below;

(a) a torque is generated due to the friction between elements;

(b) wear is produced on the contacting portion (especially on the inner peripheral edge of the sealing plate) during the utilization of the bearing. This leads to the leakage of the grease and the production of the dusts or particles due to wear; and

(c) The material can be employed for the sealing plate is limited to rubber materials or resinous materials. This leads to the limitation of the application of the bearing.

(2) As for the bearing including a sealing structure such as the oil seal (the seal of contacting type), or the bearing including a sealing structure of the non-contacting type such as labyrinth seal mechanism, there is a substantial common problem that the additional space for providing such sealing means is required. This is the essential problem for the equipment necessitating the miniturization thereof. In addition, the cost for manufacturing the bearing is also increased.

In the case of the bearing adapted to be used in the spindle motor of the hard disk drive means, the function of the magnetic disk is affected seriously, if wear particles produced during rotation flow into the magnetic disk portion.

In recent years, various sealing means are proposed for preventing the particles produced within the bearing from flowing out of the bearing.

In these sealing means, although it is necessary to provide a sealing effect similar to that had been obtained by the bearing including a sealing means of contacting type, such bearing can not be adopted since it produces wear particles at the sealing contacting portion between elements.

In this connection, following structures for sealing have been adopted;

the structure in which a bearing including a sealing plate of non-contacting type at the one side thereof is used together with an additional labyrinth mechanism;

the structure in which a bearing including a sealing plate of non-contacting type at the one side thereof is used together with an additional magnetic fluid sealing mechanism; and

the structure in which a bearing including a sealing plate of non-contacting type at the one side thereof is used together with an additional magnetic fluid sealing mechanism and a labyrinth mechanism.

In these structures, additional space for installing such additional sealing mechanisms as mentioned above is required.

Additionally, the distance between bearings (bearing span) is insufficient for eliminating the harmonic vibration due to the lack of the accuracy of the rotation of the motor hub and the rigidity of assembly. The stability of the rotation is not assured. Further, it is difficult to substantially prevent the particles within the bearing from flowing out into the disk portion.

Accordingly, the object of the present invention is to improve and ascertain the non-contacting sealing function by providing dual labyrinth mechanism through incorporating an additional labyrinth mechanism into the bearing of prior non-contacting type including at the one side thereof a sealing plate.

Another object of the present invention is to provide a multi purpose bearing which can be employed not only as a bearing of inner race rotating type, but also as a bearing of outer race rotating type.

SUMMARY OF THE INVENTION

In order to achieve these and other objects, the basic structure of the bearing of the present invention includes an inner race, an outer race, and rotating bodies interposed therebetween. The bearing is provided with at least one side thereof a pair of annular inner and outer sealing plates having a central opening respectively so as to remain a slight clearance between each plate and one of the inner and outer races respectively to assure the labyrinth seal function.

Each side portion of the inner race is provided with a stepped contour including an inner shoulder of smaller diameter and an outer shoulder of larger diameter. Each side portion of the outer race is also provided with a stepped contour including an inner shoulder of smaller diameter and an outer shoulder of larger diameter. Each side portion of the bearing is adapted to be closed by a pair of annular sealing plates. Each of these plates is provided with a central opening respectively. The embodiments of the bearing of the present invention will now be described as follows.

<The First Embodiment of the Invention>

The outer peripheral portion of the inner sealing plate is secured on an inner shoulder of the outer race with leaving a slight clearance between the inner peripheral surface of the sealing plate and an inner shoulder of the inner race. Thus, the sealing plate and the inner race are prevented from contacting with each other, and a labyrinth seal function can be obtained. The inner peripheral portion of the outer sealing plate is secured by any adhesive on the outer shoulder of the inner race with leaving a slight clearance between the outer peripheral surface of the sealing plate and the outer shoulder of the outer race so as to prevent the sealing plate and the outer race from contacting with each other. Thus the labyrinth seal function can be obtained.

<The Second Embodiment of the Invention>

The inner peripheral portion of the inner sealing plate is secured by any adhesive on the inner shoulder of the inner race with leaving a slight clearance between the outer peripheral surface of the sealing plate and the inner shoulder of the outer race so as to prevent the sealing plate and the outer race from contacting with each other. Thus the labyrinth seal function can be obtained. The outer peripheral portion of the outer sealing plate is secured by any adhesive on the outer shoulder of the outer race with leaving a slight clearance between the inner peripheral surface of the sealing plate and the outer shoulder of the inner race so as to prevent the sealing plate and the inner race from contacting with each other. Thus the labyrinth seal function can be obtained.

<The Third Embodiment of the Invention>

The outer peripheral portion of the inner sealing plate is secured by any adhesive on the inner shoulder of the outer race with leaving a slight clearance between the inner peripheral surface of the sealing plate and the inner shoulder of the inner race so as to prevent the sealing plate and the inner race from contacting with each other. Thus the labyrinth seal function can be obtained. The outer peripheral portion of the outer sealing plate is also secured by any adhesive on the outer shoulder of the outer race with leaving a slight clearance between the inner peripheral surface of the sealing plate and the outer shoulder of the inner race so as to prevent the sealing plate and the inner race from contacting with each other. Thus the labyrinth seal function can be obtained.

<The Fourth Embodiment of the Invention>

The inner peripheral portion of the inner sealing plate is secured by any adhesive on the inner shoulder of the inner race with leaving a slight clearance between the outer peripheral surface of the sealing plate and the outer shoulder of the inner race so as to prevent the sealing plate and the outer race from contacting with each other. Thus the labyrinth seal function can be obtained. The inner peripheral portion of the outer sealing plate is also secured by any adhesive on the outer shoulder of the inner race with leaving a slight clearance between the outer peripheral surface of the sealing plate and the outer shoulder of the outer race so as to prevent the sealing plate and the outer race from contacting with each other. Thus the labyrinth seal function can be obtained.

<The Fifth Embodiment of the Invention>

The inner race of this embodiment includes only one shoulder, and the inner peripheral portion of the inner sealing plate is secured thereon by any adhesive with leaving a slight clearance between the outer peripheral surface of the sealing plate and the inner shoulder of the outer race so as to prevent the sealing plate and the outer race from contacting with each other. Thus the labyrinth seal function can be obtained. The diameter of the inner peripheral portion of the outer sealing plate is same as or larger than the diameter of the shaft bearing bore of the inner race. The outer peripheral portion of the outer sealing plate is secured by any adhesive on the outer shoulder with leaving a slight axial clearance between the end surface of the inner race and the surface of the outer sealing plate opposing thereto so as to prevent the sealing plate and the inner race from contacting with each other. Thus the labyrinth seal function can be obtained.

<The Sixth Embodiment of the Invention>

The outer peripheral portion of the inner sealing plate is secured by any adhesive on the inner shoulder of the outer race with leaving a slight clearance between the inner peripheral surface of the sealing plate and the shoulder of the inner race so as to prevent the sealing plate and the inner race from contacting with each other. Thus the labyrinth seal function can be obtained therebetween. The diameter of the inner peripheral portion of the outer sealing plate is same as or larger than the diameter of the shaft bearing bore of the inner race. The outer peripheral portion of the outer sealing plate is secured by any adhesive on the outer shoulder with leaving a slight axial clearance between the end surface of the inner race and the surface of the outer sealing plate opposing thereto so as to prevent the sealing plate and the inner race from contacting with each other. Thus the labyrinth seal function can be obtained.

<The Seventh Embodiment of the Invention>

The outer race includes only one shoulder, and the outer peripheral portion of the inner sealing plate is secured thereon by any adhesive with leaving a slight clearance between the inner peripheral surface of the sealing plate and the inner shoulder of the inner race so as to prevent the sealing plate and the inner race from contacting with each other. Thus the labyrinth seal function can be obtained. The diameter of the outer peripheral portion of the outer sealing plate is same as or smaller than that of the outer race. The inner peripheral portion of the outer sealing plate is secured by any adhesive on the outer shoulder with leaving a slight axial clearance between the end surface of the outer race and the surface of the outer sealing plate opposing thereto so as to prevent the sealing plate and the outer race from contacting with each other. Thus the labyrinth seal function can be obtained.

<The Eighth Embodiment of the Invention>

The outer race includes only one shoulder, and the outer diameter of the outer sealing plate is same as or slightly smaller than that of outer race. The inner peripheral portion of the inner sealing plate is secured on the inner shoulder of inner race by any adhesive with leaving a slight clearance between the outer peripheral surface of the sealing plate and the shoulder of the outer race so as to prevent the sealing plate and the outer race from contacting with each other. Thus the labyrinth seal function can be obtained. The inner peripheral portion of the outer sealing plate is secured by any adhesive on the outer shoulder of inner race with leaving a slight axial clearance between the end surface of the outer race and the surface of the outer sealing plate opposite thereto so as to prevent the sealing plate and the outer race from contacting with each other. Thus the labyrinth seal function can be obtained. The advantages of the present invention

The following advantages can be obtained by a pair of sealing plates of non-contacting type incorporated into the end portion or portions of the bearing per se.

(a) The sealing effect will be increased substantially relative to the bearing of the prior art including one sealing plate of the non-contacting type.

(b) The leakage of the grease contained in the bearing through the non-contacting portion of the sealing plate can be avoided, and the performance on the rotation of the bearing can be improved.

(c) The conventionally required space for installing the labyrinth seal additionally to the bearing no longer necessary.

(d) It is possible to make the equipment employing the bearing of the present invention compact, to reduce the space required for installing the bearing, and to decrease the cost for making the equipment.

(e) It is possible to substitute the bearing of the present invention for the bearing of the prior art of contacting type, for the purpose of increasing the reliability.

(f) In the case that the double seal bearing of the present invention is incorporated into the motor of the hard disk drive means, particles within the bearing are prevented from flowing into the magnetic disk by means of the labyrinth seal function of the bearing. In this connection, it is not necessary to provide additional labyrinth seal and/or magnetic fluid seal.

Further, it is also possible to increase the bearing span. In conclusion, the disadvantages or problems associated with the bearing of the prior art can be eliminated once and for all by the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Further feature of the present invention will become apparent to those skilled in the art to which the present invention relates from reading the following specification with reference to the accompanying drawings, in which:

FIG. 1 is an elevational view showing a double seal bearing of the first embodiment of the present invention;

FIG. 2 is a longitudinal cross sectional view showing the double seal bearing as shown in FIG. 1;

FIG. 3 is a longitudinal cross sectional view showing a double seal bearing of the second embodiment of the present invention;

FIG. 4 is a longitudinal cross sectional view showing a double seal bearing of the third embodiment of the present invention;

FIG. 5 is a longitudinal cross sectional view showing a double seal bearing of the fourth embodiment of the present invention;

FIG. 6 is a longitudinal cross sectional view showing a double seal bearing of the fifth embodiment of the present invention;

FIG. 7 is a longitudinal cross sectional view showing a double seal bearing of the sixth embodiment of the present invention;

FIG. 8 is a longitudinal cross sectional view showing a double seal bearing of the seventh embodiment of the present invention;

FIG. 9 is a longitudinal cross sectional view showing a double seal bearing of the eighth embodiment of the present invention;

FIG. 10 is a perspective view showing annular sealing plates adapted to be incorporated into the double seal bearing of the present invention;

FIG. 11 is a longitudinal cross sectional view showing the bearing of non-contacting type of the prior art;

FIG. 12 is a longitudinal cross sectional view showing the bearing of contacting type of the prior art.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The first embodiment of the bearing of the present invention will now be described with reference to FIGS. 1 and 2.

In the structure of the bearing as shown in these figures, the bearing includes an inner race 1, an outer race 2, and a rotating body such as balls 3 retained between inner and outer races by means of retainer 4. Each side portion of the inner race 1 is provided with stepped contour including an inner shoulder 1 a of smaller diameter and an outer shoulder 1 b of larger diameter. Each side portion of the outer race 2 is also provided with stepped contour including an inner shoulder 2 a of smaller diameter and an outer shoulder 2 b of larger diameter. Each side portion of the bearing is adapted to be closed by a pair of annular sealing plates 5 and 6 such as those shown in FIG. 10. Each of these plates 5 and 6 is provided with a central opening 5 a, 6 a respectively.

In the first embodiment of the present invention as shown in FIG. 2, the outer peripheral portion of the inner sealing plate 5 is secured by any adhesive on the inner shoulder 2 a of the outer race 2 with leaving a slight clearance (a) between the inner peripheral surface of the sealing plate 5 and the inner shoulder 1 a of the inner race 1. Thus, the sealing plate and the inner race are prevented from contacting with each other, and a labyrinth seal function can be obtained.

The inner peripheral portion of the outer sealing plate 6 is secured by any adhesive on the outer shoulder 1 b of the inner race 1 with leaving a slight clearance (b) between the outer peripheral surface of the sealing plate 6 and the outer shoulder 2 b of the outer race 2 so as to prevent the sealing plate and the outer race from contacting with each other. Thus the labyrinth seal function can be obtained.

In the structure of the bearing of the second embodiment of the present invention as shown in FIG. 3, the inner peripheral portion of the inner sealing plate 5 is secured by any adhesive on the inner shoulder 1 a of the inner race 1 with leaving a slight clearance (c) between the outer peripheral surface of the sealing plate 6 and the inner shoulder 2 a of the outer race 2 so as to prevent the sealing plate and the outer race from contacting with each other. Thus the labyrinth seal function can be obtained. The outer peripheral portion of the outer sealing plate 6 is secured by any adhesive on the outer shoulder 2 b of the outer race 2 with leaving a slight clearance (d) between the inner peripheral surface of the sealing plate 6 and the outer shoulder 1 b of the inner race 1 so as to prevent the sealing plate and the inner race from contacting with each other. Thus the labyrinth seal function can be obtained.

In the structure of the bearing of the third embodiment of the present invention as shown in FIG. 4, the outer peripheral portion of the inner sealing plate 5 is secured by any adhesive on the inner shoulder 2 a of the outer race 2 with leaving a slight clearance (a) between the inner peripheral surface of the sealing plate 5 and the inner shoulder 1 a of the inner race 1 so as to prevent the sealing plate and the inner race from contacting with each other. Thus the labyrinth seal function can be obtained.

The outer peripheral portion of the outer sealing plate 6 is also secured by any adhesive on the outer shoulder 2 b of the outer race 2 with leaving a slight clearance (d) between the inner peripheral surface of the sealing plate 6 and the outer shoulder 1 b of the inner race 1 so as to prevent the sealing plate and the inner race from contacting with each other. Thus the labyrinth seal function can be obtained.

In the structure of the bearing of the fourth embodiment of the present invention as shown in FIG. 5, the inner peripheral portion of the inner sealing plate 5 is secured by any adhesive on the inner shoulder 1 a of the inner race 1 with leaving a slight clearance (c) between the outer peripheral surface of the sealing plate 5 and the inner shoulder 2 a of the outer race 2 so as to prevent the sealing plate and the outer race from contacting with each other. Thus the labyrinth seal function can be obtained.

The inner peripheral portion of the outer sealing plate 6 is also secured by any adhesive on the outer shoulder 1 b of the inner race 1 with leaving a slight clearance (b) between the outer peripheral surface of the sealing plate 6 and the outer shoulder 2 b of the outer race 2 so as to prevent the sealing plate and the outer race from contacting with each other. Thus the labyrinth seal function can be obtained.

In the structure of the bearing of the fifth embodiment of the present invention as shown in FIG. 6, the inner race and the outer sealing plate are substantially different from those of embodiments 1-4.

In other words, the inner race 1 of this embodiment includes only one shoulder 1 c, and the inner peripheral portion of the inner sealing plate 5 is secured thereon by any adhesive with leaving a slight clearance (c) between the outer peripheral surface of the sealing plate 5 and the inner shoulder 2 a of the outer race 2 so as to prevent the sealing plate and the outer race from contacting with each other. Thus the labyrinth seal function can be obtained.

The diameter of the inner peripheral portion of the outer sealing plate 6 is same as or larger than the diameter of the shaft bearing bore of the inner race. The outer peripheral portion of the outer sealing plate 6 is secured by any adhesive on the outer shoulder 2 b with leaving a slight axial clearance (e) between the end surface of the inner race 1 and the surface of the outer sealing plate 6 opposing thereto so as to prevent the sealing plate and the inner race from contacting with each other. Thus the labyrinth seal function can be obtained.

In the structure of the bearing of the sixth embodiment of the present invention as shown in FIG. 7, the outer peripheral portion of the inner sealing plate 5 is secured by any adhesive on the inner shoulder 2 a of the outer race 2 with leaving a slight clearance (a) between the inner peripheral surface of the sealing plate 5 and the shoulder 1 c of the inner race so as to prevent the sealing plate and the inner race from contacting with each other. Thus the labyrinth seal function can be obtained therebetween.

The diameter of the inner peripheral portion of the outer sealing plate 6 is same as or larger than the diameter of the shaft bearing bore of the inner race 1. The outer peripheral portion of the outer sealing plate 6 is secured by any adhesive on the outer shoulder 2 b with leaving a slight axial clearance (e) between the end surface of the inner race 1 and the surface of the outer sealing plate 6 opposing thereto so as to prevent the sealing plate and the inner race from contacting with each other. Thus the labyrinth seal function can be obtained.

In the structure of the bearing of the seventh embodiment of the present invention as shown in FIG. 8, the outer race 2 includes only one shoulder 2 c, and the outer peripheral portion of the inner sealing plate 5 is secured thereon by any adhesive with leaving a slight clearance (a) between the inner peripheral surface of the sealing plate 5 and the inner shoulder 1 a of the inner race 1 so as to prevent the sealing plate and the inner race from contacting with each other. Thus the labyrinth seal function can be obtained.

The diameter of the outer peripheral portion of the outer sealing plate 6 is same as or smaller than the outer diameter of the outer race. The inner peripheral portion of the outer sealing plate 6 is secured by any adhesive on the outer shoulder 1 b with leaving a slight axial clearance (f) between the end surface of the outer race 1 and the surface of the outer sealing plate 6 opposing thereto so as to prevent the sealing plate and the inner race from contacting with each other. Thus the labyrinth seal function can be obtained.

In the structure of the bearing of the eighth embodiment of the present invention as shown in FIG. 9, the outer race 2 includes only one shoulder 2 c, and the outer diameter of the outer sealing plate 6 is same as or slightly smaller than that of outer race. The inner peripheral portion of the inner sealing plate 5 is secured on the inner shoulder 1 a of inner race 1 by any adhesive with leaving a slight clearance (c) between the outer peripheral surface of the sealing plate 5 and the shoulder 2 c of the outer race 2 so as to prevent the sealing plate and the outer race from contacting with each other. Thus the labyrinth seal function can be obtained.

The inner peripheral portion of the outer sealing plate 6 is secured by any adhesive on the outer shoulder 2 of outer race 2 with leaving a slight axial clearance (f) between the end surface of the outer race and the surface of the outer sealing plate 6 opposite thereto so as to prevent the sealing plate and the outer race from contacting with each other. Thus the labyrinth seal function can be obtained.

In the above mentioned embodiments, although a pair of inner and outer sealing plates 5 and 6 are adapted to be provided on both sides of the bearing body, these sealing plates can be provided on one side of the bearing body. In such a case, the opposite side of the bearing body can be provided with a sheet of sealing plate of contacting or non-contacting type, or no plates are provided.

In the illustrated embodiment, although rotating bodies are shown as balls of the boll bearing, rollers (in the case of roller bearing) can also be utilized. Further, the present invention can be applied equally to the needle bearing and the fluid journal bearing.

The bearing in accordance with the present invention can be applied to many kind of motors. In particular, the bearing of the present invention can be employed as a bearing of the motor of the hard disk drive means, or a bearing of the pivot shaft of the swing arm of the hard disk drive means.

While particular embodiments of the present invention have been illustrated and described, it should be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. 

What is claimed is:
 1. A double seal bearing including an inner race, an outer race, and rotating bodies interposed therebetween, wherein: at least one of the ends of the outer race is provided with a first stepped contour on an inner peripheral surface thereof, said first stepped contour including an inner shoulder of smaller diameter and an outer shoulder of larger diameter, at least one of the ends of the inner race is provided with a second stepped contour on an outer peripheral surface thereof, said second stepped contour including an inner shoulder of larger diameter and an outer shoulder of smaller diameter, and a pair of flat annular inner and outer sealing plates including a central opening are provided on at least one of the ends of the bearing, the sealing plates are dimensioned to provide a slight clearance between outer or inner peripheral surfaces, respectively, of respective plates and one or the other of the inner and outer races, respectively, so as to provide a labyrinth seal function.
 2. The double seal bearing according to claim 1 wherein the outer peripheral portion of the inner sealing plate is secured on the inner shoulder of the outer race by an adhesive with leaving a slight clearance between the inner peripheral surface of the inner sealing plate and the inner shoulder of the inner race so as to prevent the sealing plate and the inner race from contacting with each other to assure the labyrinth seal function, and wherein the inner peripheral portion of the outer sealing plate is secured on the outer shoulder of the inner race by an adhesive with leaving a slight clearance between the outer peripheral surface of the outer sealing plate and the outer shoulder of the inner race so as to prevent the sealing plate and the outer race from contacting with each other to assure the labyrinth seal function.
 3. A double seal bearing according to claim 1 wherein the inner peripheral portion of the inner sealing plate is secured on the inner shoulder of the inner race with leaving a slight clearance between the outer peripheral surface of the inner sealing plate and the inner shoulder of the outer race so as to prevent the sealing plate and the outer race from contacting with each other to assure the labyrinth seal function, and wherein the outer peripheral portion of the outer sealing plate is secured on the outer shoulder of the outer race with leaving a slight clearance between the inner peripheral surface of the outer sealing plate and the outer shoulder of the inner race so as to prevent the sealing plate and the inner race from contacting with each other to assure the labyrinth seal function.
 4. A double seal bearing according to claim 1 wherein the outer peripheral portion of the inner sealing plate is secured on the inner shoulder of the outer race with leaving a slight clearance between the inner peripheral surface of the inner sealing plate and the inner shoulder of the inner race so as to prevent the sealing plate and the inner race from contacting with each other to assure the labyrinth seal function, and wherein the outer peripheral portion of the outer sealing plate is also secured on the outer shoulder of the outer race with leaving a slight clearance between the inner peripheral surface of the outer sealing plate and the outer shoulder of the inner race so as to prevent the sealing plate and the inner race from contacting with each other to assure the labyrinth seal function.
 5. A double seal bearing according to claim 1 wherein the inner peripheral portion of the inner sealing plate is secured on the inner shoulder of the inner race with leaving a slight clearance between the outer peripheral surface of the inner sealing plate and the inner shoulder of the outer race so as to prevent the sealing plate and the outer race from contacting with each other to assure the labyrinth seal function, and wherein the inner peripheral portion of the outer sealing plate is secured on the outer shoulder of the inner race with leaving a slight clearance between the outer peripheral surface of the outer sealing plate and the outer shoulder of the outer race so as to prevent the sealing plate and the outer race from contacting with each other to assure the labyrinth seal function.
 6. The double seal bearing according to claim 1 wherein said outer shoulder of larger diameter of said one or both ends of the outer race has a diameter larger than said smaller diameter of said inner shoulder of said one or both ends of the outer race, and said inner shoulder of larger diameter of said one or both ends of the inner race has a diameter larger than said smaller diameter of said outer shoulder of said one or both ends of the inner race.
 7. The double seal bearing according to claim 6 wherein said annular inner and outer sealing plates have edges at respective inner and outer diameters thereof, one of said sealing plates mounted to provide a clearance between an edge at one of said outer and inner diameters thereof and an outer shoulder of one of said inner and outer races, the other of said sealing plates mounted to provide a clearance between an edge at one of said outer and inner diameters thereof and an inner shoulder of the other of said inner and outer races.
 8. The double seal bearing according to claim 7 wherein said outer sealing plate is mounted to provide a clearance between an edge at said outer diameter thereof and said outer shoulder of said outer race, and said inner sealing plate is mounted to provide a clearance between an edge at said inner diameter thereof and said inner shoulder of said inner race.
 9. The double seal bearing according to claim 6 wherein each of said inner and outer sealing plates is adhesively mounted to a respective one of said inner and outer races while leaving a slight clearance to the other of said inner and outer races.
 10. The double seal bearing as recited in claim 1, wherein said inner race comprises: a first outer surface at a first diameter; a first inner race shoulder formed with said first outer surface; said first inner race shoulder having a second surface at said larger inner race diameter to form said inner shoulder of said inner race; said larger diameter of said inner shoulder of said inner race being smaller than said first diameter of said first outer surface, and a second inner race shoulder formed with said second surface; said second inner race shoulder having a third surface at said smaller inner race diameter to form said outer shoulder of said inner race; said smaller diameter of said outer shoulder of said inner race being smaller than said larger diameter of said inner shoulder of said inner race; said stepped contour of said inner race formed of said first, second and third surfaces thereof.
 11. The double seal bearing as recited in claim 10, wherein said outer race comprises: a first inner surface at a second diameter; said second diameter being larger than said first diameter of said first outer surface of said inner race; said first inner surface of said outer race substantially facing said first outer surface of said inner race; a first outer race shoulder formed with said first inner surface; said first outer race shoulder substantially facing said inner shoulder of said inner race and having a fourth surface at said smaller outer race diameter to form said inner shoulder of said outer race; said smaller diameter of said inner shoulder of said outer race being larger than said second diameter of said first inner surface, and a second outer race shoulder formed with said fourth surface; said second outer race shoulder substantially facing said outer shoulder of said inner race and having a fifth surface at said larger outer race diameter to form said outer shoulder of said outer race; said larger diameter of said outer shoulder of said outer race being larger than said smaller diameter of said inner shoulder of said outer race; said stepped contour of said outer race formed of said first, fourth and fifth surfaces thereof.
 12. The double seal bearing as recited in claim 1, wherein said outer race comprises: a first inner surface at a first diameter; a first outer race shoulder formed with said first inner surface; said first outer race shoulder having a second surface at said smaller outer race diameter to form said inner shoulder of said outer race; said smaller diameter of said inner shoulder of said outer race being larger than said first diameter of said first inner surface, and a second outer race shoulder formed with said second surface; said second outer race shoulder having a third surface at said larger outer race diameter to form said outer shoulder of said outer race; said larger diameter of said outer shoulder of said outer race being larger than said smaller diameter of said inner shoulder of said outer race; said stepped contour of said outer race formed of said first, second and third surfaces thereof.
 13. A double seal bearing including an inner race, an outer race, and rotating bodies interposed therebetween wherein the one or both of the ends of the outer race is provided on its inner peripheral surface with an inner shoulder of smaller diameter and an outer shoulder of larger diameter, the one or both of the ends of the inner race is provided on its outer peripheral surface with an shoulder, and a pair of annular inner and outer sealing plates having an central opening respectively are provided, said inner sealing plate being secured on the one of the inner and outer races with leaving a slight clearance between the inner sealing plate and the other of the inner and outer races so as to prevent the sealing plate and the inner or outer race from contacting with each other to assure the labyrinth seal function, the diameter of the inner peripheral edge of said outer sealing plate being same as or larger than that of the shaft bearing bore of the inner race, the outer peripheral portion of the outer sealing plate being secured on the outer shoulder of the outer race with leaving a slight axial clearance between the inner peripheral surface of the outer sealing plate and the end surface of the inner race so as to prevent the sealing plate and the inner race from contacting with each other to assure the labyrinth seal function.
 14. A double seal bearing according to claim 13 wherein the inner peripheral portion of the inner sealing plate is secured on the shoulder of the inner race with leaving a slight clearance between the outer peripheral surface of the inner sealing plate and the inner shoulder of the outer race so as to prevent the sealing plate and the outer race from contacting with each other to assure the labyrinth seal function.
 15. A double seal bearing according to claim 13 wherein the outer peripheral portion of the inner sealing plate is secured on the inner shoulder of the outer race with leaving a slight clearance between the inner peripheral surface of the inner sealing plate and the shoulder of the inner race so as to prevent the sealing plate and the inner race from contacting with each other to assure the labyrinth seal function. 